Have you loaded the special file: 'sihp1000.img' into /etc/printer ? During boot, you will see (and hear) mandrake load this driver into the printer; the printer will go through it's initialization routine. The file can be had by downloading the windoze driver package from HP, and unzipping it. Without this file, mandrake (and cups) cannot talk to the printer.
If you have already done all these things, then I'm clueless!
BTW, Mandrake is the only linux distro I've found (so far) that supports the HP 1000, with it's goofy GDI drivers.